Remove unnecessary threading concerns from VrMetricsHelper.

chrome/browser/android/vr_shell/vr_usage_monitor.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_ANDROID_VR_SHELL_VR_USAGE_MONITOR_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_VR_USAGE_MONITOR_H_
 
-#include "base/threading/platform_thread.h"
+#include <memory>
+
+#include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_observer.h"
 
 namespace vr_shell {
 
 enum class VRMode {
   NO_VR = 0,
   VR_BROWSER = 1,     // VR Shell.
@@ skipping 25 matching lines @@
   // config members:
   // time between stop and start to count as same session
   base::TimeDelta maximum_session_gap_time_;
 
   // minimum time between start and stop to add to duration
   base::TimeDelta minimum_duration_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionTimer);
 };
 
-// Most methods of this class are not threadsafe - they must be called
-// on the Browser's main thread.  This happens by default except for
-// SetWebVREnabled and SetVRActive, where we'll post a message to get to the
-// correct thread.
-// Destruction must happen on the main thread, or there could be corruption when
-// WebContentsObserver unregisters itself from the web_contents_.
-// There are DCHECKS to ensure these threading rules are satisfied.
-class VrMetricsHelper : public content::WebContentsObserver,
-                        public base::RefCountedThreadSafe<VrMetricsHelper> {
+// This class is not threadsafe and must only be used from the main thread.
+class VrMetricsHelper : public content::WebContentsObserver {
  public:
   explicit VrMetricsHelper(content::WebContents*);
-
+  ~VrMetricsHelper() override;
   void SetWebVREnabled(bool is_webvr_presenting);
   void SetVRActive(bool is_vr_enabled);
 
+ private:
   // WebContentObserver
   void MediaStartedPlaying(const MediaPlayerInfo& media_info,
                            const MediaPlayerId&) override;
   void MediaStoppedPlaying(const MediaPlayerInfo& media_info,
                            const MediaPlayerId&) override;
   void DidFinishNavigation(content::NavigationHandle*) override;
   void DidToggleFullscreenModeForTab(bool entered_fullscreen,
                                      bool will_cause_resize) override;
 
- protected:
-  friend class base::RefCountedThreadSafe<VrMetricsHelper>;
-  ~VrMetricsHelper() override;
-
-  void SetWebVREnabledOnMainThread(bool is_webvr_presenting);
-  void SetVRActiveOnMainThread(bool is_vr_enabled);
-
   void SetVrMode(VRMode mode);
   void UpdateMode();
 
   std::unique_ptr<SessionTimer> mode_video_timer_;
   std::unique_ptr<SessionTimer> session_video_timer_;
   std::unique_ptr<SessionTimer> mode_timer_;
   std::unique_ptr<SessionTimer> session_timer_;
 
   VRMode mode_ = VRMode::NO_VR;
 
   // state that gets translated into vr_mode:
   bool is_fullscreen_ = false;
   bool is_webvr_ = false;
   bool is_vr_enabled_ = false;
 
   int num_videos_playing_ = 0;
   int num_session_navigation_ = 0;
   int num_session_video_playback_ = 0;
 
   GURL origin_;
-
-  // not thread safe, so ensure we are on the same thread at all times:
-  base::PlatformThreadId thread_id_;
 };
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_VR_USAGE_MONITOR_H_